.\"	$OpenBSD: timingsafe_bcmp.3,v 1.2 2014/06/21 20:22:15 tedu Exp $
.\"
.\" Copyright (c) 2014 Google Inc.
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\" $FreeBSD$
.Dd August 15, 2016
.Dt TIMINGSAFE_BCMP 3
.Os
.Sh NAME
.Nm timingsafe_bcmp
.Nd timing-safe byte sequence comparisons
.Sh SYNOPSIS
.In string.h
.Ft int
.Fn timingsafe_bcmp "const void *b1" "const void *b2" "size_t len"
.Sh DESCRIPTION
The
.Fn timingsafe_bcmp
function compares the first
.Fa len
bytes pointed to by
.Fa b1
and
.Fa b2 .
.Pp
Additionally, the running time is independent of the byte sequences compared,
making it safe to use for comparing secret values such as cryptographic MACs.
In contrast,
.Xr bcmp 3
and
.Xr memcmp 3
may short-circuit after finding the first differing byte.
.Sh RETURN VALUES
The
.Fn timingsafe_bcmp
function returns 0 or not zero if the byte sequence pointed to by
.Fa b1
compares equal to or not equal to (respectively)
the byte sequence pointed to by
.Fa b2 .
.Sh SEE ALSO
.Xr bcmp 3
.Sh STANDARDS
The
.Fn timingsafe_bcmp
function is a non-standard extension.
.Sh HISTORY
The
.Fn timingsafe_bcmp
function first appeared in
.Ox 4.9 ,
.Fx 12.0 ,
and macOS 10.12.1.
